When should I worry?

So DD is 6 months on wed. She can't roll back to front or front to back, she can't sit unassisted. I'm starting to panic! She can roll from her side to her front but can't get on her side unassisted.
She is happy, healthy weight, BF, eating 2 meals of solids a day, sleeping 6pm-6am with 1-2 resettles (she dropped her overnight feed about 2 weeks ago of her own accord), sleeps 3-4 hours during the day.
She will happily play on her tummy for up to 20 min, then cry because she can't roll. "Swims" her arms & legs but goes nowhere. On her back she kicks & waves her arms, but just can't roll!
When does this become an issue? Should I look into seeing a Paed or wait a bit longer? I'm just worried cos she is getting a flat head - she needs to get moving! Seems like all the other babies her age are doing something at least 😣

Hmm I must have a very advanced mothers group then. Oldest is 6.5 months, youngest 4.5 months 80% would be rolling, 50% sitting unaided if placed in a sitting position. There are even 2 crawlers!
Feeling like I should be doing more to encourage DD to move.

It sounds very normal to me, just make sure they get lots of floor time.

Your baby sounds a bit past this stage but I was given advice from a child physio to encourage a baby to roll put them on their back on the floor and tickle their tummy. Their legs will go in the air. If you keep doing this then at some point they will overbalance to one side and presto, stage 1 of a roll.

Flat heads can be an issue if not managed appropriately though (I went through this with my DS). Is the flat spot at the back of the head? If so, encourage baby to look either side more when lying down. When they are asleep counter position their head so they are not resting on their flat spot. This was the key thing I had to do with DS (he strongly favoured looking to his right) and every time he slept I had to counter position his head.

My DD rolled at about 7 months and was walking steadily and unaided one day after she turned 11 months. She was the last one at my mothers group to roll, but the first to walk so you really can't read too much into comparisons with other babies (as you are no doubt aware!)

Thanks for reassuring me!
The flat spot is at the back - we did physio until 4 months because she used to favour one side, now she sleeps facing straight up.
She is not tall, actually more short & round - like her mum!

I was looking through our videos the other day to find out when our 1st bub started moving. He didn't crawl, he did a single-leg-kick and slide on his tummy. And he started that at about 8.5-9months. He started crawling shortly after his 1st birthday and started walking independently at 19 months. I think he was late to develop because he was a big BF bub with an even bigger head. I've read that big bubs have more to move so are generally later to get moving.

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